Process for synthesis of resins containing unsaturations of the (meth) acrylic type to be cured by radiation or heat and used for powder paints

ABSTRACT

Resins comprising (meth)acrylic unsaturations are obtained by reacting functional groups of unsaturated monomers without solvents at temperatures above 150° C. and under controlled heat exchange, while maintaining intact their unsaturations, with functional groups of saturated and/or unsaturated polymers. The technologies and the work cycles used for conventional resins may also be used for these resin types.

Owing to known strong homopolymerization tendency of acrylic monomers inorder to yield polymers comprising acrylic unsaturations, relatively lowtemperatures are used (in the range of 60 to 130° C.; at most 150° C.)together with suitable amounts of polymerization inhibitors and byadding solvent in order to lower polymer viscosity. In this way, uniformmass heating is favoured and local superheating, which would cause thepolymerization of unsaturated functionalities, is avoided.

Several processes, working either in the presence of solvents or atrelatively low temperatures together with short reaction times to yieldpolymers comprising unsaturated groups for powder paints, are known.

EP 0249306 (Autotype Int.Appl.)discloses an unsaturated polymer obtainedin toluene solution wherefrom it is precipitated and filtered. EP0636669 and EP 0644905 (DSM) disclose polymers obtained at temperaturesof 50 to 110° C. in butylacetate solution or toluenetxylene solutionfollowed by solvent stripping at 150° C. EP 0650978 (BASF) disclosesunsaturated polymers obtained without solvents, but homogenized byextruding reactive compounds together with unsaturated functionalmonomers at temperatures up to 130° C. for a short time (7-15 min).

These limitations in temperatures and time impair the possibility ofusing the synthesis. However, many manufactures of resins for powderpaint are in the need of carrying on, also for these types of resins,the use of technologies and work cycles used for conventional resinssuch as polyesters and acrylics, which are manufactured at temperaturesabove 150° C., up to 260° C., and unloaded at temperatures between 160and 220° C. for a relatively long time (0.5-8 hours) dependent upon theresin amount and the crushing rate of the flaking machine. However, forthe above stated reasons, that has not been possible up to now.

It has now surprisingly been found possible to add an unsaturatedfunctional monomer to a resin comprising reactive functional groups,maintained at temperatures in the range of 150° C. to 200° C. and withan addition of suitable inhibitor amounts, and to react it with theresin for 50 to 60 minutes without affecting the resin unsaturation.

This object is achieved by supplying the reaction mass with heat inorder to avoid local superheating. This in practice occurs bymaintaining the temperature in the range of values reached during theexothermic reaction or slightly higher without the need of addingsolvents.

Starting polymers usable for the purposes of this invention may beeither acrylic resins or saturated or unsaturated polyesters havingreactive groups such as hydroxy, carboxylic, glycidyl, isocyanategroups, whereas (meth)acrylics comprising functional groups mentionedabove are especially used as reactive monomers.

The unsaturated functional monomers are preferably selected from thegroup consisting of glycidyl(meth)acrylate, (meth)acrylic acid,methacrylisocyanate, benzo-1-(1-isocyanate-1-methyl)-4,1-methenyl,isocyanateethylmethacrylate or unsaturated isocyanate adducts.

Polymerization inhibitors are conventional inhibitors such ashydroquinone, hydroquinone-monomethylether, mono-ter-butylhydroquinone,phenotiazine, diethylhydroxylamine,diphenyl-p-phenylenediamine,isopropyl-phenyl-p-phenylenediamine,triphenylphosphite.

The process of this invention will now be described, but not limited bythe following examples, wherein the term “parts” is to be intended as“parts by weight”.

EXAMPLE 1

In a four-neck flask provided with a thermometer, a stirrer, adistillation column and an inert gas bubbling inlet, 1500 parts ofAlftalat AN 725 (carboxylic polyester provided by Hoechst and havingNA=30-36, cone-plate viscosity of 4000-7000 mPas/200° C., Tg=63-69° C.)were loaded. The resin was melted at 180° C. and thereafter 250 parts ofglycidyl methacrylate together with 1 part of hydroquinone were addeddropwise and under stirring for 20 minutes. This temperature wasmaintained through mild heating until NA=3 and cone-plate viscosity of1120 mPas/200° C. were reached. Thereafter the temperature was broughtto 170° C. and the mass was maintained at this temperature for 3 hourswithout having gelation followed by its unloading and its cooling. Theobtained product had NA=1.5 and cone-plate viscosity of 1680 mPas/200°C., Tg=40° C. and equivalent weight unsaturation grade of about 1000.

EXAMPLE 2

Following the same process of Example 1 850 parts of Synthacryl VSC 1438(glycidyl resin provided by Hoechst and having EEW=360-400, cone-plateviscosity of 8000-12000 mPas/170° C., Tg=46-52° C.), were loaded andafter having melted the mass at 180° C., 2.5 parts oftriphenylphosphite, 8 parts of hydroquinone and 1 parts of phenotiazinewere added. After homogenization of the resultant mass 150 parts ofmethacrylic acid were added dropwise for 10 min. After 10 minutes fromthe conclusion of the addition, the final product was examined and itwas found to have NA=1 and cone-plate viscosity of 2600 mPas/200° C. Thetemperature of 180° C. was maintained for another hour and after thistime the mass was unloaded. The obtained product was found to haveNA=0.5, cone-plate viscosity of 3400 mPas/200° C., softening point of80-85° C., equivalent weight unsaturation grade of about 575.

EXAMPLE 3

In a 5 liter reactor provided with a thermometer, a stirrer and an inertgas bubbling inlet 620 parts of ethyleneglycol, 150 parts ofneopentyleneglycol, 1328 parts of terephthalic acid and 2 parts ofmonobutylstannoic acid were loaded. Therefore the mass was heated at240° C. in order to obtain hydroxy saturated polyester having NOH ofabout 200. The polyester was cooled at 170° C. and 441 parts of maleicanhydride and 0.4 parts of hydroquinone were added, followed by heatingat 200° C. until an unsaturated polyester having NA=50, cone-plateviscosity of 1440 mPas/200° C. and softening point of 80-85° C. wasobtained. Thereafter the product was cooled at 180° C. and at thistemperature 300 parts of glycidilmethacrylate together with 1 part ofhydroquinone were added for 10 min. After 15 minutes the product wasexamined and it was found to have NA=0.8 and cone-plate viscosity of1000 mPas/200° C. The mass was maintained at 180° C. for further 8 hoursand after its cooling the product had NA=0.8, cone-plate viscosity of1320 mPas/200° C., softening point of 80-85° C. and equivalent weightunsaturation grade of about 380.

EXAMPLE 4

In a 5 l reactor provided with a thermometer, a stirrer, a distillationcolumn and an inert gas bubbling inlet 1507 parts of 1,4-butanediol,2098 parts of fumaric acid and 2.7 parts of monobutylstannoic acid wereloaded. Therefore the mass was heated at 120° C. in order to obtain anunsaturated polyester having NA=108 and cone-plate viscosity of 160mPas/200° C. and after cooling at 170° C., 1.4 parts of hydroquinone and388 parts of glycidylmethacrylate were added. After 10 minutes theproduct was examined and it was found to have NA=51 and cone-plateviscosity of 160-200° C. The mass was mantained at 170° C. for further 4hours and after this time the product was unloaded and an unsaturatedcristalline polymer having MP of 75-80, cone-plate viscosity of 140mPas/200° C., NA=41 and unsaturated equivalent weight of about 90, wasobtained.

EXAMPLE 5

In a 5 l reactor provided with a thermometer, a stirrer and a refluxcondenser 320 parts of dimethylmaleate were loaded and the mass washeated at 150° C. Thereafter a blend consisting of 880 parts of styrene,100 parts of methacrylic acid, 440 parts of metylmethacrylate, 300 partsof butylacrylate and 20 parts of di-ter-amyl peroxyde was added dropwisefor 6 hours. After the addition was completed the product was mantainedat 170° C. for 1 hour and then brought under vacuum until a solidresidue >95%, NA=31.6, cone-plate viscosity of 21120 mPas/200° C. andTg=55° C., were obtained. Then 4 parts of triphenylphosphite, 10 partsof hydroquinone and 1 part of phenotiazine were loaded. Afterhomogenization 180 parts of glycidilmethacrylate were added for 10minutes. The product was maintained at 170° C. and after 1 hour it wasfound to have NA=7 and cone-plate viscosity of 7040 mPas/200° C. Afterfurther 2 hours at 170° C. the product was unloaded and cooled. It wasfound to have NA=2, cone-plate viscosity of 800 mPas/200° C., Tg=44° C.

APPLICATION TESTS

1.UV Hardening

The resins produced in the above examples were used according to thefollowing composition for powder paint by using UV-rays hardening:

Resin: 92%

Flow promoter* 5%

UV photoinitiator 3%

* Master Additol XL 496 (hydroxy EW 85%+polyacrylate 15%)

The paint composition comprising the resin of the example 2 contains LH746 (polyurethaneacrylate provided by Hoechst) as co-crosslinking agentwith a resin/co-crosslinking agent ratio corresponding to 70/30.

A twin screw extruder was used for these application tests under thefollowing conditions:

Temperature zone (° C.): 80-100-100 Feed (%): 20 Rotation speed (rpm):300

The obtained paints were applied by using a corona gun and the film washardened on a dinamic UV-IR oven provided with ten IR 230V/800W lampsand two 80 W/cm UV lamps.

For the acceptance tests Al metal sheets and MDF wooden panels wereused. Acceptance test results:

Properties Example 1 Example 2 Example 3 Example 4 Example 5 acetone 3 21 3 5 resistence 24h 2-3 2-3 5 1-2 5 stability at 35° C. impact test 14<6 10 <6 <6 on MDF panel Joule

5: negative 4: insufficient 3: sufficient 2: moderate 1: good

2. IR Hardening

By using Perkadox SB as thermic initiator, the resin of the example 5showed a gelation time corresponding to 58 s at 180° C. The sameinitiator was used to examine the resin of the Example 3 with thefollowing composition:

Resin: 92% Flow promoter  5% IR catalyst  3%

The extrusion conditions were the same as the above stated ones. Thecrosslinking conditions corrisponded to a single passage through the IRlamps area at 0.5 m/min. Acetone resistence resulted moderate.

What is claimed is:
 1. A process for making solid resins which comprisesreacting: a. saturated and/or unsaturated polymers or polycondensateshaving a glass transition temperature (Tg) of ≧30° C. or a melting pointof ≧80° C., comprising one or more reactive functional groups permolecule, said polymers being solid at room temperature; and b.unsaturated monomers comprising a functional group which is able toreact with functional groups of said polymers or polycondensates, at atemperature above 150° C. without solvents, said reaction beingconducted in the presence of polymerization inhibitors which maintainunsaturations, and under heat exchange, said reaction forming saidresins in a solid form, and said solid resins having a glass transitiontemperature (Tg) of ≧30° C. or a melting point of ≧80° C. and comprising(meth) acrylic unsaturations.
 2. Process according to claim 1 whereinthe polymers and the polycondensates are selected from the groupconsisting of acrylic resins, saturated polyesters, unsaturatedpolyesters, vinyl resins and epoxy resins.
 3. Process according toclaims 1 or 2 wherein the polymers and the polycondensates comprisereactive groups selected from the group consisting of hydroxy,carboxylic, anhydride, glycidyl and isocyanate groups.
 4. Processaccording to claim 1 wherein the unsaturated monomers are(meth)acrylates comprising functional groups selected from the groupconsisting of hydroxy, carboxylic, anhydride, glycidyl and isocyanategroups as functional groups.
 5. Process according to claims 1 or 4characterized in that the unsaturated monomers are selected from thegroup consisting of glycidyl (meth)acrylate, (meth)acrylic acid,methacrylisoocyanate, benzo-1-(1-isocyanate-1-methyl)-4,1-methenyl,isocyanateethylmethacrylate or unsaturated isocyanate adducts.